Process for spinning polyacrylonitrile filament having low degree of crimp and high cimp reversibility



June 13, 196L J. F. RYAN, JR. ETAL 2,988,420

PRQCESS FOR SPINNING POLYACRYLONITRILE FILAMENT mvzuc LOW DEGREE OF CRIMP AND HIGH CRIMP REVERSIBILITY Filed Feb. 16, 1959 3 Sheets-Sheet 1 Ez'g, 1

R .0 RN J E H N m T M 6R U Mm. R T R $5 MB O JR J1me 1951 J. F. RYAN, JR.. ETAL 2,983,420

PROCESS SPINNING POLYACRYLONITRILE FILAMENT HA LOW DEGREE OF CRIMP AND HIGH CRIMP REVERSIBILITY 3 Sheets-Sheet 2 Filed Feb. 16, 1959 v INVENTORS JAMES FRANCIS RYAN, JR. ROBERT LAUREN TICHENOR RESIDUAL SOLVENT June 13, 1961 J F Filed Feb. 16, 1959 RYAN, JR.. EI'AL 2,988,420

PROCESS FOR SPINNING POLYACRYLONITRILE FILAMENT HAVING LOW DEGREE OF CRIMP AND HIGH CRIMP REVERSIBILITY Eig 3 Sheets-Sheet 5 68l0l2 l4 |s|a2o 2224 s AS-SPUN DENIER PER mum INVENTORS JAMES FRANCIS RYAN, JR. ROBERT LAUREN TICHENOR Unite States This invention relates to synthetic textile fibers and particularly to improved crimped composite filaments and a process of making them.

In the course of the development of the synthetic textile fiber industry, much effort has been expended towards the production of fibers which retain the well-known advantages of synthetic fibers such as ease-of-care, durability, and improved mechanical properties, but which, at the saime time, possess the properties required to obtain fabrics of outstanding aesthetic appeal such, for example, as that which characterizes Wool fabrics. Wool fabrics have good bulk and cover, obtainable at a relatively low finishing shrinkage which is quite desirable from an economic standpoint. In addition, wool fabrics have excellent elastic properties such as stretchability, compressional resilience, and liveliness, and display a pleasing surface handle. Finally, the surface of wool fabrics is renewable; even after such severe deformations as crushing or glazing, a new surface can easily be obtained, for example, by wetting, steaming, or mere recovery inhumid air.

Although different proposals of the prior art have attained one or more characteristics of wool fabrics, in no instance have such synthetic materials been properly considered as being wool-like in other than superficial appearance.

It has been proposed to improve fabric properties by imparting to the synthetic fibers a spiral crimp. Fibers of this type have been prepared by use of special spinning conditions or after-treatments which bring about differential physical properties overthe cross section of singlecomponent filaments, or by spinning together two or more materials to form a composite filament, i.e., one which contains the components in an eccentric relationship over the cross section of the filaments. If the twocomponents of a composite filament possess substantially different shrinkage, a crimp is caused bythe differential shrinkage of the spun and drawn components.

More recently, it has been proposed to produce crimped composite filaments of synthetically formed polymers having the capacity of changing the amount of crimp upon being exposed to the e'lfect of a swelling agent and upon reverting to the original crimp upon removal of the swelling agent. This characteristic is, for convenience, referred to as reversible crimp and is observed by the squirming of the filaments upon both application and removing of the swelling agent. The value of this crimp reversibility is evidenced by the ability of the filaments in yarns, when embodied in a fabric, to squirm or twist around in the fabric under the influence of a swelling agent such as water (and also on removal of the swelling agent), but, nevertheless, to regain the original crimp in the fabric with removal of the swelling agent, as by drying. Fabrics containing these filaments acquire a high degree of fullness or covering power as a result of the swelling treatment and retain or even increase this fullness after being subjected to such treatments repeatedly. Since the finishing shrinkage is low,the yarns of fabrics containing such filaments have a relatively open structure so that the fabrics exhibit unusual elastic properties.

However, it has been found that the high degree of crimp reversibility in the fibers necessary to produce yarns atent Patented June 13, 1961 IQC frequency leads to a harsh raspy handle in knit-wear and woven-wear fabrics and to staple processing difiiculties resulting in poor yarn uniformity and high yarn shrinkage.

It is an object of this invention to produce a crimped, composite filament having a level of crimp reversibility sufficiently high to afford good recovery from compaction, and the development of good bulk and covering power in fabrics while having a crimp level that affords a pleasing wool-like handle in fabrics.

Another object of this invention is to provide a process which will reduce the crimp level in a composite filament while retaining a given degree of crimp reversibility.

In accordance with the present invention a composite filament is prepared having 10 to 18 helical crimps per inch of extended length and having an equilibrium crimp reversibility of 25 to 50%.

The process of the invention requires the simultaneous spinning of two fiber-forming compositions into a composite filament, and its extrusion into a spinning cell under conditions which afford a rapid setting-up of the fiber structure. The composite filament due to the eccentric relationship of its components and their composition will be capable of crimping from the straight state upon shrinkage and will have crimp reversibility.

In a preferred embodiment of the invention, the polymeric components are positioned so that the edge of the composite filament comprising the lower shrinking component faces the center of the spinning cell and 'the edge of the filament comprising the higher shrinking component faces the periphery of the spinning cell.

In a further embodiment of the process, a less concentrated spinning solution is used for the polymer that yields the lower shrinking homofilament than is used for the other polymeric component.

By the expression conditions which afford a rapid setting-up of the fiber structure is meant high gas and cell temperatures, high gas flow rates and slow spinning speeds. These conditions result in a low residual solvent content in the yarn when dry-spinning. In the process of the invention there is obtained a residual solvent content in the range of 13 to 27% for 8 denier per filament (d.p.f.) (0.85 Tex) as-spunfibers. The residual solvent content obtained for other deniers can be readily estimated from FIGURE 8 in which curve 1 shows the maximum permissible residual solvent content as a function of filament denier and curve 2 displaced from curve 1 in FIGURE 8 illustrates the preferred residual solvent content for the various filament deniers.

The crimp reversibility of the filaments of this invention is determined by the following test.

A single filament is separated from the single end or tow of drawn, unrelaxed fibers. A three-inch length of the filament is attached to opposite sides of a rectangular copper wire frame with 30% slack between the ends. The rack and filament is then boiled off for 15 minutes to develop the crimp. The crimped filament is then transferred to a special viewing holder by ta ping or gluing the ends so that about 10% slack is present and the filament length between the clamped ends is approximately 2.5 inches. The filament and viewing holder are then mounted vertically in a stoppered test tube containing desiccant. The tube is stored vertically overnight (18-24 hours) at 70 C. Following this conditioning period to dry the filament the tube is then brought to room temperature (approximately 25 C.). After allowing 30 minutes for cooling, the total number of crimps in the No. of erirnps (25 dry)-No. of erimps (70 Wet) X 100 ECR: No. of erimps' (25 dry) Alternatively the actual change in crimps/inch of extended length from 25 C. dry to 70 C. wet expressed as A c.p.i. may be used and is calculated as follows:

A p i (ECR) (orirnps, dry, per inch of ex tended length) By extended length is meant the length of a filament or yarn as measured under sufficient tension to pull out of the crimp and give an essentially straight filament or yarn. All crimp counts are stated in terms of extended length.

Another property of the filaments of this invention that is of great importance is their ability to recover from compaction. The following test is used to measure this property.

Crimped fibers were cut in 2-inch lengths, hand carded and made into pellets weighing 0.20 gram. The pellets were placed into a cylinder (0.5 inch diameter hole) under a freely sliding piston that exerted 1,000 p.s.i. for two minutes. The height of the pellet under compression was measured. Compressed pellets of the same fiber were removed from the cylinder and: (I) allowed to recover in dry air overnight and then (2) exposed to steam at atmospheric pressure for minutes. The heights of the recovered pellets were measured after treatments '1' and 2 and the recovery from compaction calculated:

Compressed height of pellet Recovery For purposes of illustration, the invention will be described in terms of dry spinning of polymers from acrylonitrile in dimethylformamide (DMF) in a particular type of dry spinning cell. It will be obvious to those skilled in the art that the apparatus and processes can be widely modified in view of the teaching of this invention.

A closed spinning cell is used comprising a cylindrical cell surmounted by a spinning head, means for circulating an evaporative medium through the cell which enters through the spinning head around the threadline, means for extruding the solution through the spinneret in the head, and means for withdrawing the yarn through the bottom of the cell. The spinning head used is similar to that shown in US. 2,615,198 issued to G. N. Flannagan. The term head temperature when hereafter used means the temperature of the gas as it issues from the gas heater and before it enters the spinning cell. By the expression cell temperature is meant the inside temperature of the wall of the spinning cell.

Referring to the drawings:

FIGURE 1 is a central cross-sectional elevation of a spineret assembly which can be used to make the composite filaments of this invention;

FIGURE 2 is a transverse cross-sectional plan view of the apparatus of FIGURE 1 taken at 2-2 thereof and showing details of the top of the back plate;

FIGURE 3 is a transverse cross-sectional plan view taken at 33 of FIGURE 1 showing details of the bottom of the back plate;

FIGURE 1A is an enlarged portion taken from FIG- URE 1 to show details of the spinneret at the spinning orifice; and

FIGURE 4 is a central cross-section elevation of a spinneret assembly which can be used to extrude 3 concentric circles of composite filaments.

FIGURES 5, 6, and 7 show greatly magnified cross sections, i.e., sections perpendicular to the filament axis, of typical filaments of this invention produced by dry spinning. In these drawings one components is shade to show the separation between components.

With reference to FIGURE 1, the bottom spinneret plate 2 which-contains a circle of orifices 3. is held in place against back plate 1 by retaining rings 12 and 14 and by bolt 13. A fine-mesh screen 4 e.g., 200 mesh per inch, is pressed into position between, and serves as a spacer between, spinneret plate 2 and back plate 1. Back plate 1 contains two annular chambers 8 and 9 whichare connected to suitable piping and filtration apparatus (not shown) to receive different spinning compositions. Lead holes 11 go from annular chamber 9 to annular space 7. Lead holes 10 lead from annular chamber 8 to annular space 6. Annular spaces 6 and 7 are separated by wall 5 which is disposed above orifices 3 and spaced from spinneret plate 2 by screen 4 to permit free and contiguous passage of the spinning fluids from annular spaces 6 and 7 through orifices 3, the mesh of screen 4 being fine enough to permit spinning fiuid passage through orifices 3, as shown in detail in FIGURE 1A.

In FIGURE 2 are shown four lead holes 10 and four lead holes 11 equally'spaced within the concentric chambers 8 and 9, respectively.

In FIGURE 3 are shown the concentric inner and outer annular spaces 6 and 7 and the fine-mesh screen 4 partially in section.

Operation of the described apparatus in the practice of this invention is readily understood. Separate spinning materials are supplied to the inner annular chamber 9 and outer annular chamber 8, respectively, of the back plate; the former flows from chamber 9 through the lead vholes 11 into the inner annular space 7 and thence through screen 4 and orifice 3 to form a part of a composite filament, while the latter passes through the lead hole 10 to the outer annular space 6 and thence through screen 4 and the outer side of the orifice 3 to form the other part of the composite filament.

The expression intrinsic viscosity with the symbol (n) as used herein signifies the value of ln (n) at the ordinate axis intercept (i.e., when c equals 0) in a graph of as ordinate with 0 values (grams per ml. of solution) as abscissas. (n) is a symbol for relative viscosity, which is the ratio of the flow times in a viscosimeter of a polymer solution and the solvent. ln is the logarithm to the base e. All measurements on polymers containing acrylonitrile combined in the polymer molecule were made with DMF solutions at 25 C.

EXAMPLE I This example shows the preferred process and product of this invention.

A 20% solution in DMF of polyacrylonitrile of (n) 1.95 and containing 27 milliequivalents of acid groups per kilogram of polymer (as determined by titration in a DMF solution) (hereinafter designated polymer A) was FIGURE 1 and thence to annular space 7 and out into the spinning cell (9 inches in diameter by 14 feet long) as part of a composite filament so that it faces the center of the spinning cell. Simultaneously, a 27% solution in DMF of a copolymer of acrylonitrile and styrenesulfonic acid 9,6/4% by weight composition of (n) 1.54 and analyzing 240 milliequivalents of acid per kilogram of polymer (hereafter designated polymer B) was fed to annular space 8 (47 grams/minute) and then through annular space 6 to be extruded as the other component of a composite filament so that it faced the wall of the spinning cell. The spinneret contained 140 orifices of 0.0069 inch in diameter located on a 5.27 inch diameter circle. A mixture of carbon dioxide and nitrogen gases was circulated through the cell at a rate of 57 lbs. per

90 C. and measuring percent of this stress redeveloped on drying shows the following results:

The product of Example I was dyed with a basic dye by immersion in a dye bath at 50 C., heating to the boiling point in a period of minutes and then holding at the boiling point for 30 minutes. The dye bath comprised an aqueous solution containing the following:

Table I Item Component 1 Component 2 Draw Denier Crimps 1 Crimp Recovery, Ratio per inch ECR Steamed 1(I1)txemple AN 2.0 AN/BBA 96/4 1.5 210 4.0 3 10 40 375 2--. Algl'g/lgfi/fSA 1.5 AN/SSA 1.5 150 4.0 3 22 215 a ANl.--l.' 2.0 AN/SSA 95 5 2.0 318 8X 6 so 19 360 4 AN/SSA 98.5I1.5 2.0 AN/SSA 97.2/2.8.. 2.0 70 8 3 10 18 145 5 ANIMA/SSA AN/MA/SSA 1 5 60 4.5 3 10 19 140 1 Per inch of extended length.

hour. Temperatures of 105, 315, 180 C. were used for Percent the spinning solutions, head and cell respectively. The threadline consisting of 140 composite filaments was wound up at 200 y.p.m. and contained 19% of DMF and 1.0% water based on its dry weight.

Three hundred fifty ends of yarn produced as above with a combined denier of 382,000 were combined into .a tow and drawn to 4 times their original length (i.e.,

4 draw ratio) in baths of water at 95 C. which extracted the residual DMF. The drawn and unrelaxed wet tow was mechanically crimped in a stuffer box similar to that shown in Hitt US. 2,747,233 to an extent of 6-7 herringbone crimps per extended inch using a stuffer box temperature of 50 C. The crimped tow was then cut into 3% length staple. The cut staple, loosely arranged in a tray, was dried for 15 :minutes in a circulating air oven at 270275 F. The dried staple had a weak mechanical crimp of 6 to 7 crimps per inch plus 6-8 helical crimps per inch.

The above prepared staple develops 16 helical crimps per inch of extended length when boiled free of restraint in water. The helically crimped fibers thus prepared have an ECR of 40% and a A c.p.i. of 6.4 crimps per inch. Substantially 'all of the mechanical crimp is removed. The staple has a tenacity of 2.2 grams per denier (g.p.d.) and an elongation at the break of 40% and a denier per filament of 3.0 (0.34 Tex) after boiling and drying.

EXAMPLE II The properties of the product of thisinvention as made in Example I are compared with the properties .of other composite fibers in Table I below. It will be noted that the fiber of Example I meets the requirements of the present invention since it has a high crimp reversibility (ECR of or larger) coupled with a low crimp intensity (10 to 18 crimps per inch of extended length). Data listed in Table I for other fibers not made by this process show that a reduction in crimp is accompanied by a reduction in crimp reversibility.

A further significant improvement of this property is .the recovery from compaction after steaming which is most clearly shown .by comparing the data in Table I for item 1 with items 2, 4, and 5.

, Crimp development force measured by ,Instron stressing of single filaments at 0.015 g.p.d., then wetting out at Astrazone red 6B Synthetic Dyes, vol. II, pg. 1174, by K. Venkataraman (Academic Press, Inc., N.Y.,

The ratio of bath to fiber was maintained at 50:1. The fiber dyed to a bright uniform red shade.

When fiber prepared by spinning the polyacrylonitrile solution (homopolymer) of Example I into single component filaments was dyed in a similar bath, the fiber dyed to a weak, non-uniform pale pink shade.

It was surprising that the composite fiber aiforded deep, relatively bright dye shades.

Similar results were obtained with other basic (cationic) dyes.

Staple fibers corresponding to items 1-5 in Table I were spun into similar yarns (60 Tex, 8.5Z, woolen system) and fabrics knitted. The bulk (cm. /gram) .of the fabrics with a similar construction (coursesX the fabrics.

Bulk Handle flne wool-like, resilient. harsh.

very harsh.

soft, moderate loft. soft, thin.

The advantages of the product of this invention (item 1) are apparent.

EXAMPLE III the cell respectively in the composite filaments. Temspectively.

filaments are exposed to higher temperatures.

peratures of 110, 330, and 180 were used for the solution, head, and cell temperature respectively. The gas was conducted through the cell at a rate of 80 lbs. per

hour. The yarn (8.8 d.p.f. 1.0 Tex, as-spun) was Wound up at 375 y.p.m. and 350 combined tows then drawn 4.5 as in Example I.

B. A second spin was conducted that was identical in all respects to the first with the notable exception that the position of the two polymeric solutions was reversed so that polymer A was extruded so as to face the outside of the spinning cell.

The two products obtained from part III A and part III B had 24.9 and 32.0 crimps per inch after boiling in water, and ECRs of 24% and 21% respectively. The as-spun yarn of III A and IH B contained 30.5 and 29.5% of DMF respectively.

When single component filaments are spun and drawn under the same conditions, polymer B has the greater shrinkage (e.g., 24% vs. 22% for polymer A).

The above spins were repeated with all conditions being the same with the exception that the spinning speed was reduced to 200 y.p.m. and feeds of solutions were reduced (53 and 53 grams per minute for solutions of polymer A and polymer B respectively) to give the same denier. The staple produced from the spin (III C) in which polymer A was located on the inside of the threadline had 13.7 crimps per inch upon boil-off while the staple produced from the other spin (III D) with the position of that polymer reversed had 16.2 crimps per inch upon boil-01f. The as-spun yarn of III C and III D contained 20.3 and 22.0% DMF respectively.

The above spins also demonstrate the fact that a lower crimp level is obtained at lower spinning speeds.

o 7 EXAMPLE IV v This example illustrates the importance of spinning speed on the process of this invention.

-head and cell respectively were used. The gas was conducted through the cell at a rate of 80 lbs. per hour and the yarn wound up at 200 y.p.m. After drawing the yarn 4.5x, cutting and drying as in Example I the 3 d.p.f. staple developed 176 crimps per inch upon boil- When the above spin was repeated with all conditions being the same with the exception that the spinning speed was raised to 375 y.p.m. and solution feed rate correspondingly increased staple (3 d.p.f.) having a boiled-01f crimp level of 26.9 crimps per inch was ob- .tai ned. The speeds of 200 and 375 y.p.m. gave as-spun yarns containing 22.4 and 41.4% DMF respectively, and

having as-spun deniers per filament of 8.8 and 8.8 re- Obviously higher speeds can be used if the EXAMPLE V with the exception that the spinning cell was 7 inches in diameter by 14 feet long and the spinneret had 0.059" diameter orifices located in 3 concentric circles containing 84, 84, and 84, orifices in the outer, middle and inner circles respectively.

A 21.5% solution in DMF of polymer A was fed to annular space 15 (157 grams/minute) (FIGURE 4) so that the polymer solution was extruded as the component facing the cell center in the outermost and the innermost circle of filaments while a 28.5% solution in DMFof v.polymer B was fed to annular space 16 (157 grams/ minute) so that'this polymer formed the component of a composite fiber facing the wall of the spinning cell on the outer and inner circles of filaments while facing the center of the cell on the middle circle of filaments. The gas was conducted through the cell at a rate of 81.6 lbs. per hour and temperatures of 110, 345, and 195 C. were used on the solution, head, and cell respectively. The yarn (7.8 d.p.f.) was wound up at 350 y.p.m., drawn 4X, cut and dried as in Example I to give 3 d.p.f. staple.

In a second run, all conditions were maintained the same with the exception that the concentration of polymer A was increased to 23.5%.

The staple from the spin with the lower polymer concentration had 14.5 crimps per inch upon boil-off While the staple from the higher polymer concentration had 17.4 crimps per inch after boil-off.

The change to lower concentrationin the spinning soluticn of the polymer yielding the lower shrinking homofilament is preferably accompanied by an increase in the (n) of the polymer to maintain the viscosity of the spin ning solution at the desired level.

EXAMPLE VI Using the equipment of Example V, a 23.5% solution in DMF of polymer A was extruded (147 grams/minute) so as to face the cell wall in the outer edge of filaments and a 28.5% solution in DMF of polymer B was extruded (147 grams/minute) so as to face the center of the cell in the outer ring of filaments. The gas was conducted through the cell at a rate of 81.6 lbs. per hour. Temperatures used were 110, 280, and 182 C. for the solution, head, and cell respectively. The yarn was wound up at 350 y.p.m., drawn 4.0x, cut and dried and relaxed as in Example I to give a 3 d.p.f. staple with 22.6 crimps per inch after boiling in water.

When the above spin was repeated with all conditions being the same with the exception that the head temperature was raised to 345 C. the 3 d.p.f. staple upon boilofi had 17.4 crimps per inch and the DMF content of the as-spun yarn was lowered from 37.9 to 25%.

EXAMPLE VII This example illustrates the critical elfect of the rate of fiow of the evaporative medium in the spinning cell.

The two polymer solutions of Example VI were extruded in the same manner as in Example VI with temperatures of 110, 345, and 182 C. for the solution, head, and cell temperatures respectively and the yarn wound up at 350 y.p.m. In one instance the gas was conducted through the spinning cell at a rate of 64.5 lbs. per hour while in the second instance the gas Was conducted through the cell at a rate of 81.6 lbs. per hour. After a 4X draw, drying andboil-off as in Example I a 3 d.p.f. staple with 19.7 crimps per inch was obtained from the first spin while the second staple (3 d.p.f.) spun at the higher aspiration rate contained only 17.4 crimps per inch. The use of the higher flow rate of gas reduced the DMF content of the as-spun yarn from 29.6% to 25 EXAMPLE VIII This example illustrates the critical selection of the cell 0 temperature.

Using the solutions, apparatus and conditions of Example V (i.e., 21.5% solution of polymer A and 28.5% solution of polymer B at 157 and 157 grams/minute respectively) and the same spinning conditions with the exception that the cell temperature was C. composite filaments were obtained after drawing 4x and relaxing having 21.0 crimps per inch. The use of a higher cell temperature of C. with all other conditions being the same reduced the crimp intensity of the composite filament to 14.5 crimps per inch. Residual solvent content of the two as-spun yarns (7.8 d.p.f.) were 29 (est.) and 24 (est.) percent respectively for 170 and 195 C. WhenExaInple I is repeated with all conditions the same assume 9 except for raising the cell temperature to 210 C. filaments having 10 helical crimps per inch and ECR of 35% are obtained. The as-spun yarn contains 14% DMF.

EXAMPLE IX The procedure of Example I was followed with the replacement of the acrylonitrile homopolymer with a 94/6 mixture of the acrylonitrile homopolymer and a copolymer of acrylonitrile and styrenesulfonic acid (96/4%) to give a total acidity in the blended polymer of 45 meq. of acid groups per kilogram of polymer. The differential ionic content between the blended polymer and the copolymer Was 195 meq./kg. The final staple fiber had a denier per filament of 2.9, a tenacity of 2.1 g.p.d. and an elongation of 31% and had 15 helical crimps per inch of extended length after bo'iling ofi. The ECR was 34%. t

The physical properties of the fiber of this example and that of Example I were considered to be essentially equivalent. The fibers were subjectively evaluated in knit tubing and the aesthetics of the fibers were judged to be equivalent and very satisfactory.

Carded two-gram samples of scoured staple were pot boiled for various lengths of time up to 4 hours in the following Black dye bath (all percentages based on weight of fiber):

3.06% 0.1. Basic Yellow 11 5.04% 0.1. Basic Red 13 4.32% Basic Orange of Example VH1 (11) US 2,821,526 1.68% CI. Basic Green 4 5.0% a long chain alkyl trimethyl ammonium bromide 12.5% sodium sulfate 0.5% sodium acetate/acetic acid buffer (pH=) Dye bath-to-fiber ratio was 100/1 and fiber was added after the bath had been brought to the boil.

After dyeing, the fibers were scoured in a 2% solution of a non-ionic surfactant (the condensation product of polypropylene glycol and ethylene oxide) at the boil for 15 minutes, rinsed, centrifuged, dried, and carded for visual comparisons of dye quality.

The brightness and depth of shade improved steadily with time. Cross sections of these fibers of Example I showed: that in the first two hours of dyeing, the acid modified component accepts dye very rapidly and the unmo'dified side (homopolymer) does not accept dye across its skin barrier in this time interval. The dye that is present in the unmodified side enters it across the polymer-polymer interface in the composite filament. After four hours it was noted that the dye had penetrated further into the unmodified side from the polymer-polymer interface and that there was definite evidence of skin dyeing. The fact that the unmodified side obtained any dye whatsoever in this process was quite surprising since its great reluctance to dye is well known. The four-hour dyeing time gave deep, relatively bright black shades.

The fibers of this example show greater dye penetration across the polymer-polymer interface and a greater tendency to ring dye. At equal lengths of dyeing time, the fiber of this example gives a brighter black than did the fiber of Example I.

The dyeings were repeated using dyes equivalent to 7.3, 11.0, and 14.6% dye based on the fiber weight. In the case of Example I fibers the highest level of dye was needed in order to get bright dark acceptable blacks with this dye procedure. Surprisingly enough, the fibers of this example gave bright black shades at levels of 7.3, and 11% dye that were equivalent to the 14.6% dye level on the other fiber. Single component filaments made of the polymer blend (45 meg/kg. total acidity) are only dyed to light shades by the above procedures.

A convenient and economical way to produce the fibers of this example consists of blending the acrylonitrile homopolymer with or more of its weight of waste stock of the composite filaments obtained in spin- 10 ning the fibers of this example and then spinning a solution of this blend with a solution of the acidic copolymer as indicated above.

Suitable polymers for use in this invention can be found in all classes of linear fiber-forming polymers that have a solubility such that they can be dry spun. The two polymers selected must have the required difference in shrinkage and in swellability so that the composite filament crimps and a reversible crimp results. Suitable polymers, methods for selecting them, and crimping methods are described in coassigned and copending Taylor application, Serial No. 640,722 filed February 18, 1957. The following is a brief description of such subjeot matter:

Either component of the composite, crimp reversible filaments of this invention can be found in many groups of synthetic addition polymer materials. The necessary differential reversible length change between the components is readily obtained by altering the content of ionizable groups in the two polymers.

Such ionizable groups are readily obtained by copolymerizing acrylonitrile, for example, with monomers containing acid groups such as .carboxylic, sulfonic or phosphonic in either the salt or free-acid form.

The following sudfonated polymerizabl-e monomers and their salts are eminently suited for use in this invention: p-styrenesulfonic Iacid, methallylsulfonic acid, allylsulfonic acid and ethylenesulfonic acid.

It will be obvious to those skilled in the art that the required ionizable groups can be incorporated into a polymeric component by the blending of 2 or more polymers. The polymers should preferably be compatible Vinyl polymers other than acrylonitrile polymers can be used in this invention which, although not having the required reversible length change per se, can be modified by acidic or basic modifiers as suggested above, so that the copolymers do have the required reversible length change.

The inclusion of from 115% of certain non-ionic modifiers in copolymers of .acrylonitrile enhances the effect of any ionizable groups present in the final polymer. In general, it has been found that the monomers that are effective in this connection are also the same monomers which, when incorporated into :an acrylonitrilc polymer increase the dyeability of fibers made therefrom with a disperse dye, such as the blue-disperse dye Prototype 62.

Among the more desirable monomers from the point of view of enhancing the effect of ionizable group content are methyl acrylate, methyl methacrylate, methyl vinyl ketone, acrylamide, N-tertiarybutylacrylamide, vinyl methoxyethyl ether, methoxyethyl acrylate and vinyl acetate.

While the inclusion of as little as 1% of one of the above monomers enhances the reversible length change effect of the ionizable groups contained in that polymer, generally from 3 to 10% is desired.

The composite filaments of this invention are charaoterized in that at least one of the components contains at least 50 milliequivalents of an ionizable group per kilogram of polymer. It is preferred that one component, in addition to containing at least 50 milliequivalents, contains a substantial excess of ionizable groups over the other component where both components contain such groups. It is desired to point out, however, that the non ionic disperse dye enhancing monomers disclosed herein increase the effect of the ionizable groups in said component in proportion to the concentration of the nonionic modifier. It is therefore desired, in order to obtain the substantial effects of this invention, to make allowance, where necessary, for the non-ionic modifier content.

The selection of polyacrylonitrile (the homopolymer) of (n) 1.5 to 2.5 and a copolymer containing at least acrylonitrile from 1 to 5% of an acidic modified monomer (95 to 350 milliequivalents of acidity per kilogram of polymer) of (n) 1.0 to 2.5 is preferred. Even more preferred is the use of polyacrylonitrile and a copolymer of acrylonitrile containing sulfonic acid groups as discussed in the above cited copending application in the amount of 200 to 300 milliequivalents of acidity per kilogram of polymer. This preferred combination affords, under the processing conditions of this invention, a medium level of crimp intensity to 18 crimps per inch of extended length) that affords a pleasing handle in fabrics, a high level of crimp reversibility (25 to 50 EUR percent) which gives good recovery from compaction (300 to 400% from steaming), high bulk when incorporated into such articles as sweaters, and good dyeabil-ity with basic dyes.

The filaments of this invention can be used in the preparation of normally spun yarns, however, for some applications, e.g., yarns intended for the knitting of sweaters, displaying little or no pilling, it has been found desirable to use a high degree of twist in spinning the yarns. A twist multiplier of 2.0 to 4.0 is conveniently used in such applications as is consistent with the desired aesthetics. The twist multiplier is related to the twist (turns per inch, t.p.i.) by the following relationship:

t.p.i.=Twist multiplier X /cotton count from to the extent that the residual solvent content in the as-spun fiber is less than the amount indicated by curve 1 of FIGURE 8 of the drawings for filaments of that as-spun denier, the polymer in one of said spinning solutions being substantially polyacrylonitrile and the polymer of another spinning solution being a copolymer of acrylonitrile and from about 1 to 5% of an acid-groupcontaining monomer, said copolymer containing at least milliequivalents of an ionizable group per kilogram of copolymer.

2. A process for preparing a composite filament having from about 10 to 18 helical crimps per inch and an equilibrium crimp reversibility of from about 25 to 50% comprising simultaneously spinning at least two solutions of fiber-forming polymers into a spinning cell in the form of a composite filament and evaporating solvent therefrom to the extent that the residual solvent content in the as-spun fibers is less than the amount indicated by curve 1 of FIGURE 8 of the drawings for filaments of that as-spun denier, the polymer of one of said spinning solutions being substantially polyacrylonitrile and the polymer of another of said spinning solutions being a copolymer of acrylonitrile and from about 1 to 5% of styrenesulfonic acid said copolymer containing at least 50 milliequivalents of ionizable groups per kilogram of copolymer.

3. The process of claim 2 wherein the copolymer is extruded so that it faces the wall of the spinning cell.

4. The process of claim 2 wherein the solution used for the copolymer is more concentrated than the spinning solution used for the other component.

References Cited in the file of this patent UNITED STATES PATENTS 1,867,298 Zart July 12, 1932 2,439,814 Sisson Apr. 20, 1948 2,443,711 Sisson June 22, 1948 2,517,946 Kohorn Aug. 8, 1950 FOREIGN PATENTS 514,638 Great Britain Nov. 14, 1939 

1. A PROCESS FOR PREPARING A COMPOSITE FILAMENT HAVING FROM ABOUT 10 TO 18 HELICAL CRIMPS PER INCH AND AN EQUILIBRIUM CRIMP REVERSIBILITY OF ABOUT 25 TO 50% COMPRISING SIMULTANEOUSLY SPINNING AT LEAST TWO SOLUTIONS OF FIBER-FORMING POLYMERS INTO A SPINNING CELL IN THE FORM OF A COMPOSITE FILAMENT AND EVAPORATING SOLVENT THEREFROM TO THE EXTENT THAT THE RESIDUAL SOLVENT CONTENT IN THE AS-SPUN FIBER IS LESS THAN THE AMOUNT INDICATED BY CURVE 1 OF FIGURE 8 OF THE DRAWINGS FOR FILAMENTS OF THAT AS-SPUN DENIER, THE POLYMER IN ONE OF SAID SPINNING SOLUTIONS BEING SUBSTANTIALLY POLYACRYLONITRILE AND THE POLYMER OF ANOTHER SPINNING SOLUTION BEING A COPOLYMER OF ACRYLONITRILE AND FROM ABOUT 1 TO 5% OF AN ACID-GROUPCONTAINING MONOMER, SAID COPOLYMER CONTAINING AT LEAST 50 MILLIEQUIVALENTS OF AN IONIZABLE GROUP PER KILOGRAM OF COPOLYMER. 